This invention relates to the bulk production of alloy material by deposition from the vapour phase and in particular to the removal of deposited alloy from a collector used in such a process.
Presently evaporated alloys are produced by deposition of alloy vapour from an evaporator onto a collector. In the process described in UK Patent Application No. 819956 the collector in the form of a rotating drum is positioned above the evaporator. Both the collector and the evaporator are housed within a vacuum or low pressure chamber. An unacceptable temperature rise at the surface of the deposited alloy is prevented by a combination of controlled cooling via the internal surface of the collector and also by control of the speed of rotation of the collector itself so that a particular area of the collector surface is not exposed over-long to the evaporating metal. Under conditions of controlled cooling and speed of rotation the collector is continuously rotated above the evaporator until the required thickness of deposit is obtained. The collector is then removed from the vacuum chamber and the collector itself machined from the deposited alloy using a boring tool. The remaining deposit is then cut into arcuate plates which may be formed into sheets by conventional metal working processes.
It will be appreciated that a major problem in such a process lies with the complete destruction of the collector. If the type of collector chosen for the process does not rely on gas-gap cooling assemblies for temperature control but on more conventional forms such as pipes carrying cooling fluid for example, then the interior of the collector drum will be far from a smooth bored cylinder and will in fact represent a major item of expenditure in terms of added value in machining time on attachment points for heaters, cooling pipes and heat conduction devices etc.
The present invention provides a collector which is re-usable and which may be removed and re-installed within the vacuum chamber without a requirement to completely dismantle and re-fit the supporting shafts and temperature control equipment.
According to the present invention a collector for use in a process for the bulk production of an alloy is coated with material having a melting temperature or temperature at which the onset of fusion occurs above the peak operating temperature at the deposition surface during operation of the process, such that on completion of deposition the material between the collector surface and the deposited alloy may be melted rendering the deposited alloy detachable from the collector.
According to a feature of the invention the collector is constructed such that minor movements of the deposited alloy due to localised thermal and mechanical stresses result in flexing of the collector surface and continuous metallurgical and thermal contact between the collector surface and the deposited alloy.
Preferably the melting temperature or temperature at which the onset of fusion occurs of the coating material is below the temperature at which the onset of rapid, irreversible precipitation reactions will occur within the deposited alloy.
The deposited alloy may be removed from the collector by cutting the alloy into discrete slabs prior to removal from the collector. The cutting operation may be assisted by the provision of grooves filled with the coating material in the deposition surface of the collector corresponding to paths traversed by a cutter, thereby avoiding damage to the collector surface by the cutter. Where the collector is a drum collector the grooves preferably extend axially between the drum ends so that the deposited alloy may be cut into arcuate plates.
The coating material is preferably a solder of the eutectic type, that is, having a melting/solidification temperature as opposed to a melting/solidification temperature range. The solder is preferably applied to the surface of the collector by a spraying process such as, for example, flame or plasma-arc spraying. Where the collector is manufactured from an aluminium based material it may be necessary for the collector surface to have an initial deposit of copper to allow 'wetting' by the subsequent solder coating.